You think you know what an amplifier should sound like? Well I did, until Gerd Sauermann (in person!) brought a pair of these over from Germany to my place in the UK.

My following posts in this thread will no doubt come across as unadulterated advertising for Sauermann. And you know what? I couldn't give a damn. When someone follows their passion and produces something like this (like someone else we all know), it needs to be shouted about. Loudly.

Intriguing this amp looks to be somewhat along the lines of the First Watt F1 which provides current to the speaker in proportion to the voltage input (and so the amp delivers the required current in to the speaker regardless of what impedance it sees and impedance also changes dynamically). But it looks as though it goes further as the F1 has special requirements of the speaker (particularly the crossover) to work properly.

Hi Paul, my electronics knowledge is hazy at best but I agree, there seems to be some similarity between the two approaches. This isn't surprising as Gerd Sauermann is quite familiar with the designs of Nelson Pass.

Also, if I draw from my own experience of owning and listening to many different amplifiers, the closest I've gotten in the past to the sound I'm getting now is with my old Pass Labs Aleph 4 (now sadly no longer with me).

The Sauermann shouldn't work well with my Quads. So how come it seems to?

Well firstly, let's consider its bass. It's fuller and more extended than I've ever heard from my large Quads (the 2905s). What's interesting is that there is a 'family resemblance' to the bass with my old Pass Aleph 4 amp and also my Berning 300B amp. If we look at the 'on paper' power outputs at 4 Ohms (the impedance of the Quads below 100Hz) of these class-A amps, they're approx the following:

- Pass Aleph 4: 100W- Sauermann: 45W- Berning 300B: 6W

Could it be that this 'full and extended' bass is actually due to distortion (harmonic, or whatever else)? I mean, how could these amps be better than my Sanders Magtech amp (900W into 4 Ohms) in the bass? If this 'full and extended bass' is caused by distortion of some kind, I don't understand why it remains, even at low listening volumes.

My hypothesis is that it has something to do with an amplifier's ability to 'keep phase'. In order of bass quality, I would put these three amps in this order:

Phasure emerged from my before-XXHighEnd 2 years of developing a Local Positioning System which worked with 0.1mm accuracy. This is million$ military stuff ...

But what it really is about is the reverse of audio;It works with the phase difference of antennas (GPS works the same) which in this case works with the speed of light. So, with only two antennas but both working at a difference frequency, positioning is enabled ... in 3D and for most positions unique. All 100% unique needs two antennas more.

So ...Most positions unique with two antennas - and in the 3D space.Two speakers and such ...At some stage I will have this working. But accuracy is the subject.

This is where the Sauermann comes in.Or where the NOS1 comes in. Gerd really found me first;For a more than good reason as it appeared later ...

Hi Mani - usually the power rating of an amp will not directly have any effect on the bass performance of the speakers. Across the frequency band the speakers will take what they want from the amp driving them i.e. according to the impedance they present. The difference between amps is their ability to provide current where it is needed which is not really a function of their power rating.

But that would not be the case with a "current drive" amplifier. And this is where I am not sure if I am right that Sauermann amp delivers current into the speaker regardless of what is happening with the impedance of the speaker. But lets say for a moment that it does. It means that a big problem that most speakers suffer (i.e. that impedance varies considerably with input current) no longer matters because the amp forces in current (in direct relation to input voltage) regardless. And of course that would potentially have a dramatic improvement on sound quality because it would mean that the speaker would no longer suffer for example power compression.

But there would be problems because lets say there is an impedance increase across certain frequencies then the Sauermann would force in current which would increase volume at those frequencies (ie bass) which would not be the case with a "normal" voltage amp. So a special kind of speaker may be required to work with that type of amplifier.

And so therefore I have to think that I MUST be WRONG and that Sauermann is not a current drive amplifier because there would potentially be problems with many / most speaker designs.

So forget I said anything and we should maybe continue to wonder what is happening. BUT it would be great if Gerd reads this and could provide a little more insight into the design of his amp. Because we are a curious lot around here!!!!

As i read the design it is about a way to decouple the amplifiers current path from its voltage path. Current is kept constant at the (bottom) voltage part so it appears unloaded. This has the advantage that there is no interaction between the voltage gain and load wich is a source of distortion.

Unmentioned is the setup of the current sources. These are usually -100%- feedback powerfollowers and have very low intrinsic distortion provided the powersupply can deliver. These supplies probably float wrt the voltage maintaining a constant voltage to the currentsources. At least that would make sense given the voltage amp designprinciple.

So it is more about minimising the interaction between loads IN the amplifier than an alternative way to put current in the speaker. If I understand it well it is designed as a class A bridged voltage source.

Given the feedbackless design I expect it to have a higher output impedance than the megawatt amps. This means that any LF resonance will be audibly enforced.

The whole interplay between amps, speakers and rooms requires that it should be considered as a system. Oh and Peter just added the source component with the 0.7 magic button... . That is a whole lot of variables to take on consideration!

My 2cents on this topic,

Regards, Coen

Logged

Audio PC: XXHE PC with RAMdisk. Music PC with i5. Power cable PE not connected, together with nos1 and poweramp in separate "audio" powerstrip.

Hi Paul, hi Coen, thanks for your thoughts. Well, what ever's happening, my feeling is that the Sauermann is accentuating the bass and attenuating the treble, compared to my Sanders Magtech amp (which was designed with electrostatics in mind). Let's see if we can work through this.

But there would be problems because lets say there is an impedance increase across certain frequencies then the Sauermann would force in current which would increase volume at those frequencies (ie bass) which would not be the case with a "normal" voltage amp. So a special kind of speaker may be required to work with that type of amplifier.

I think you may actually be right (sort of). If you look at the impedance curve of the Quads, you'll see that:1. below 100Hz, they're 4 Ohms or so2. between 100Hz and 10KHz, they're pretty much 8 Ohms3. between 10-18KHz, they rise gradually to a peak of 20 Ohms or so4. above 18KHz, they dip sharply to 2 Ohms or so

It really sounds like the Sauermann is accentuating region 1 and attenuating region 3. So my only 'correction' to your post would then be that there would be a rise in volume with an impedance decrease, as opposed to increase. Does this make sense?

Given the feedbackless design I expect it to have a higher output impedance than the megawatt amps. This means that any LF resonance will be audibly enforced.

Yep. But Gerd quotes the output impedance as 50 milliOhms across the whole audio bandwidth! Hmmm...

BTW, I'm not criticizing the Sauermann amp here - it makes music in a superb way. But at this point, I'm just trying to understand why/how it could sound so different to any other amp I've heard with my Quads, and especially my Sanders amp.

I (or we) compared them to my GainClones. I consider the GainClones to be completely neutral. This is about bass, mid, high, everything. A bit dangerous within itself to state so, because first the source has to be neutral too. Well, I consider the NOS1 to be even more neutral, which I can derive from all what I feed to it, comes trough.Well, as it does that through the GainClones.

Mind you, being neutral is subjective to some extend, but let's say that the definition of it comes from no single track sounding the same. At least this is how I judge it.

Neutrality is not equal to how beautiful something can sound. However, it is dangerous to find examples where "more beautiful" would not lead to the loss of neutrality, or otherwise how the oppononent may not have been neutral after all.

In the case of the Sauermann I found no difference, except for in one area : the highs. Cymbals have more body and sing more.

The area of "highs" is dangerous within itself, because we may consider highs from digital to be wrong anyway. Or they are smeared, or they imply false harmonics, and no one way to do it 100% right exists. Still it would be so that when all tracks sound the same in this area, something along the lines is not rendered how it should be (optimally).I don't perceive such from the GainClones, and I don't think I perceived so from the Sauermanns.I must leave it to both being neutral, but the Sauermann makes a better job of it.

I did not - no, not at all perceive any decrease in highs output. However, it should be "softer" for the attacks. It "should be" because of the better colouring I perceived. But I dit NOT notice any softness.

A few days back I described how synthesized drums suddenly became apparent because of a XXHighEnd tweak. I described it as sliky in the positive sense. Beautiful. But what I added to it, was that the lot being synthesized became apparent because -as it only now appeared !!- the edge applied to those high frequency built up synth sound, had gone. This edge is not spread evenly over the whole frequency range concerned, and it comes along "here and there". Call it intermodular harmonic distortion. Things interact. This now, funnily enough, makes that synthesized drums sound more realistic; if you'd look how a cymbal disforms (in slow motion) you can imagine how often its sound changes during its envelop of the sound, and decay.With this kind of distortion out of the way, the sound becomes more refined. Ehm, more realistic, because distortion is not - no matter it may contribute to "good sound".

Nothing is more dangerous than freshness because of distortion. Sometimes hard to recognize so.

The Sauermann seems to lack the distortion that may be present in the GainClones. Well, officially GainClones *are* full of distortion. Reletively spoken of course, but this THD stuff *is* important, and what I recall from the Sauermann is that its THD figures equal that of the NOS1 (the GainClones as I have them are 6dB worse than the NOS1).

All 'n all you should try to perceive the "less highs" as just less distortion. If you can not do this, only then start digging in impedance stuff and further secrets.

... the edge applied to those high frequency built up synth sound, had gone... With this kind of distortion out of the way, the sound becomes more refined.

The first thing that struck me on listening to the Sauermann was the lack of any 'lines' delineating the individual instruments. Edges have totally gone. Instruments that used to irritate me (like loud trumpets) now sound OK... pleasant even. The initial attack, the fine detail and pin-point spatial stability are all there, but the music comes to you as a coherent whole with no edges. When a guitarist plucks a string, it's the whole guitar you hear, and not predominantly the string with a bit of disjointed body thrown in. And I don't think I've ever heard this before.

It's taking me quite a while to get used to lack of 'freshness' that I'm so used to.

As i read the design it is about a way to decouple the amplifiers current path from its voltage path. Current is kept constant at the (bottom) voltage part so it appears unloaded. This has the advantage that there is no interaction between the voltage gain and load wich is a source of distortion.

Unmentioned is the setup of the current sources. These are usually -100%- feedback powerfollowers and have very low intrinsic distortion provided the powersupply can deliver. These supplies probably float wrt the voltage maintaining a constant voltage to the currentsources. At least that would make sense given the voltage amp designprinciple.

So it is more about minimising the interaction between loads IN the amplifier than an alternative way to put current in the speaker. If I understand it well it is designed as a class A bridged voltage source.

Given the feedbackless design I expect it to have a higher output impedance than the megawatt amps. This means that any LF resonance will be audibly enforced.

Hi to all,

I'm very pleased to see that this discussionis starting in this forum. I hope I'll find some time to give replies and comments in time.Regarding the amps circuit design: On the first look it might have some similarities to Pass' circuits but in the end it differes in total due to one mayor difference which is, that there is constant current flowing through the voltage gain stage.

Hi Coen, You are pretty close but not totally right.Since there is constant current flowing through the voltage gain stage this stage has an output impedance of some kilo ohms. This stage can not deliver any power or AC current at all.The current source that is keeping the current through the voltage gain stage constant has a control loop circuit at a current gain of more then 10 million. This control circuit delivers any current the speacer draws in addition to the constant current flowing through the voltage gain stage. Due to the extremly high current gain factor of that controller loop the output impedance of a single current source drops down to as little as 6 to 7 milli ohms. So the symmetric amplifiers has an output impedance of about 15 milli ohms (which no other single stage single transistor amp can deliver).One big advantage of this circuit design is that the distortion produced is independent of frequency and load impedance. It is just related to the output voltage. The distortion spectrum remains homogenious at nearly any load and frequency change.But harmonic distortion is not the only aspect that matters. Group delay, phase shift, bandwidth etc. the entire behaviour within the time domain maters much more. And since my amps are very "fast" also at low impedance loads (1 ohm or less) - the current control loop operates at a bandwith of about 1 mega Herz, the amplifiers bandwith is above 300 kilo Herz - the behaviour within the time domain on complex (low) impedence is best. But all these electronic technical aspects are not really the main thing. We talk about reproducing the illusion of music. That is what matters. In the end you have to have the feeling that someone real is making music in your room just for you. You have to be able to feel the "puls" of the music the attitude of the artist, his "message". I tried to fine tune my amp by various means to give that illusion best. The circuit is only the basis. The next thing is the quality of the parts used and their exact values within the circuit (determined in listening sessions). Then the thermal stability and at last but not least the mechanical attributes. The cabinets of my amps and power supplies are assambled the way to be not sensitive to vibration. Every screw for instance is treated at least twice bevor being mounted. Plates are damped so that no vibration can cause any microphonic effect ....

Hi Peter,thanks for posting that link, but fairaudio did not test the latest revision of my amplifier. There are some anhancements made to eleminate vibrations that have a really significant impact on the sonic quality. The bass gained strenght and dynamic and the entire resolution capabilities of the amp did get better (even though fairaudio rated them extremly good in their test).There will be another test about the monos comming at "Hörerlebnis" in a couple of month. They will get the amps tomorrow.